The present invention relates to printed antennas, more particularly to printed antenna configurations which improve the efficiency of these antenna.
Antennas adopt many forms, each adapted for a particular application of the antenna. Antennas have many commercial and military applications such as cellular telephones and other mobile communications and data links.
One type of antenna is the dipole antenna which comprises a quarter wavelength dipole radiators coupled through a balanced transmission line and a balun to a drive signal source or a receiver. Other types include loop, slotted loops, end loaded and such like.
Various forms of dipole antennas are described for example in U.S. Pat. No. 5,387,919, U.S. Pat. No. 5,598,174, U.S. Pat. No. 5,754,145, while in the U.S. Pat. No. 3,971,125, the methods of making printed antennas using a printed circuit technique is described.
In general, it maybe seen that for dipole antennas, it is desirable to provide an arrangement wherein the feed network does not interfere with the radiation path of the antenna, and in which there is minimal unwanted radiation from the antenna. Furthermore, the antenna should have sufficient bandwidth for many types of applications and should be capable of being mounted for use without the mount interfering substantially with the radiation pattern of the antenna. Also quite importantly, the antenna should be generally inexpensive to fabricate with the capability of withstanding tolerance variations during the manufacture process while still maintaining an adequate radiation pattern.
Furthermore, for printed circuit board based high gain antenna array, a problem is the high loss due to the feed network. Traditionally, to reduce the loss of the feed network, a low loss PCB material is used in the antenna array design. However, low loss PCB material is usually more expensive than the standard FR4 material. For example, a stand FR4 material costs approximately $1.5 U.S. per square foot, but a low loss RF35 material is still about six times higher in price. Thus, it is desirable to provide for printed antennas dielectric material which is inexpensive but at the same time has a minimal effect on the characteristics of the antenna which are desired for a particular application.
The present invention thus seeks to mitigate some of the above disadvantages.
In accordance with this invention, there is provided a printed antenna comprising a dielectric substrate, dipole elements formed on a surface of the substrate, a matching network for coupling a driving point to the antenna elements, whereby common mode currents are minimized thereby minimizing the antenna performance degradation
In accordance with a further embodiment of the invention, there is provided a printed circuit antenna comprising a first substrate having antenna elements formed thereon; a second substrate material having a feed network formed thereon and for coupling a feed to the antenna elements.